1. Field of the Invention
The present general inventive concept relates to an inkjet image forming system, and more particularly, to an inkjet image forming system which can compensate for deterioration in image quality caused by the occurrence of a defective nozzle and a method of compensating for the defective nozzle in the inkjet image forming apparatus.
2. Description of the Related Art
In general, inkjet image forming apparatuses are apparatus which form an image by firing ink with a print head which is separated by a predetermined interval from a printing medium and reciprocates in a direction perpendicular to a conveying direction of the printing medium. Such an inkjet image forming apparatus which forms the image by firing the ink on the printing medium with the print head reciprocating in the direction perpendicular to the conveying direction of the printing medium is called a shuttle type inkjet image forming apparatus. The print head of the shuttle type inkjet image forming apparatus is provided with a nozzle unit including a plurality of nozzles for firing ink.
Recently, high speed printing has been implemented by using a print head having a nozzle unit corresponding to a width of a printing medium instead of a print head reciprocating in a width direction of the printing medium.
Image forming apparatuses operating in such a manner are called a line printing type inkjet image forming apparatus. In the line printing type inkjet image forming apparatus, the print head is disposed in a fixed manner, and only the printing medium is conveyed. Therefore, driving mechanisms of the line printing type inkjet image forming apparatus are simple, and printing can be implemented with high speed.
FIG. 1 is a view illustrating a print pattern at the time of occurrence of a defective nozzle in a conventional inkjet image forming apparatus, and FIGS. 2A to 2D are views illustrating a method of compensating for the defective nozzle in the conventional inkjet image forming apparatus at FIG. 1.
Referring to FIG. 1, the inkjet image forming apparatus prints an image by firing ink I on a printing medium with nozzles 82 provided to a nozzle unit 80. If some of the nozzles 82 of the nozzle unit 80 have a defect, the ink I cannot be normally fired from a defective nozzle 84, so that missing lines occur on the printing medium, as illustrated in FIG. 1. Namely, if some of the nozzles 82 have a defect, the ink I cannot be fired from the defective nozzle 84 on to printing regions of the printing medium, so that white bands such as missing lines occur. Since the white bands of an image printed on the printing medium can be easily seen, the white bands severely affect printing quality. A conventional method of compensating for the deterioration in image quality caused by such defective nozzles is disclosed in U.S. Pat. No. 5,581,284. FIGS. 2A to 2D are views illustrating a process to compensate for the defective nozzle in the conventional method of FIG. 1.
The conventional method is a method of compensating for the occurrence of a defective nozzle in an inkjet image forming apparatus. Here, the defective nozzle denotes a missing nozzle which cannot fire ink or a nozzle which cannot normally fire ink, such as a weak nozzle of which function is weakened. In the conventional method, in a case where defective monochrome (that is, black) nozzles (63 in FIG. 2A) are defected, when the defective nozzle must be used, other colors, that is, cyan, magenta, and yellow are sequentially printed on a same region which must be printed by the defective nozzle 63. An associated process is illustrated in FIGS. 2B, 2C, and 2D in which the same region is sequentially printed with cyan (FIG. 2B), magenta (FIG. 2C), and yellow (FIG. 2D) to compensate for the defective (e.g., black) nozzle. In this process, Process Black dot “P” is formed (FIG. 2D) to represent a summation of a cyan dot (FIG. 2B) and a magenta dot (FIG. 2C) followed finally by a yellow dot (FIG. 2D). In this manner, the cyan, magenta, and yellow are printed on the same region, and a color black can be represented even though the black nozzle is defective. The process is called a process Black or a process Composite Black. However, the method cannot be used in a case where nozzles firing color inks (i.e., cyan, magenta, or yellow) other than black also have a defect. In the case where any one of the nozzles used for compensation also has a defect, the compensation is performed with such colors as red (yellow + magenta), green (cyan + yellow), and blue (cyan + magenta) which are different from the process Black or Composite Black, thus severely affecting the print quality. Therefore, there is a need to improve the print quality by employing a defective nozzle compensation which can compensate not only for a defective black nozzle, but for the defect of one or more compensation nozzles (e.g., cyan, magenta, yellow).